Gaffa tape and zip tie flea bag to seat base for a soft, heated seat in the inevitably cold wet weather!I would put it head facing backwards to avoid tank teeth balls interface.
Sorry, I can't be of any real use
Maybe find a decent auto upholsterer, he should be able to supply foam cut it to shape. He could also do the seat cover although an after market cover could be a good template to help him shape it right.
